The present invention relates to the field of etching a material.
The present invention may relate more particularly to the field of the production semiconductor components, in which, during production, numerous steps are generally provided for selectively etching one material relative to another or others, to the field of recovering semiconductor substrates having defects, in which it is desired to remove a surface layer in order to recover a subjacent substrate, possibly already provided with a certain number of layers formed in a suitable way, and to the field of improving the surface state of a layer of a material.
Generally, when it is desired to remove a layer deposited on a substrate in a selective manner relative to another layer, after having possibly masked part of the layer to be removed if it is desired to remove only part thereof, two main methods exist in the field of the fabricating semiconductor components.
The first family of methods consists of “wet” etching in which the structure, one layer of which is to be etched, is immersed in an etchant, typically one based on hydrochloric or hydrofluoric acid. Several mixtures have been developed for allowing selective etching of one layer relative to another, for example a silicon oxide layer relative to a silicon nitride layer, a silicon oxide layer relative to silicon, or a metal layer relative to an insulating layer.
Within this family, document U.S. Pat. No. 6,746,967 describes a method for oxidizing nickel in an oxidizing solution at a controlled pH. Simply to accelerate oxidation, the presence of low-frequency ultrasound modifies the energy barrier necessary for the nickel to be etched by the solution.
The second family of methods, called “dry” etching, consists of placing the structure carrying the layer to be removed in a plasma containing etchants, for example radical species or active radicals of chlorine, fluorine, oxygen etc.
The second family of methods has many advantages compared with the first, notably from the fact that it permits anisotropic attack and that it often has better etching selectivity between two materials. However, it has the disadvantage of requiring complex equipment and, in the case where the layer to be etched is carried by a silicon substrate, of only making it possible to treat one or two silicon substrates at the same time. On the other hand, although the first family of methods is often impossible to put into practice when it is desired to perform highly selective etching of one material relative to another material, it has the advantage of allowing batch treatments, it being possible for many wafers to be placed in a boat and then immersed in the etching solution.
Various variants of these two families of methods are known to a person skilled in the art. For example, as regards the “wet” etching method, it is sometimes proposed to improve the result by applying an electric field between the material to be etched and the etching solution.
A third family of methods, more generally used for cleaning and degreasing surfaces, consists of immersing the surface in a cleaning bath, for example an alcohol bath, and of applying sound vibrations to the liquid medium at relatively low sound frequencies, usually of the order of 20 to 4.5 kHz. The vibrations then assist in detaching dirt particles from the surface to be cleaned.
In addition, in “wet” etching methods, mixers are normally used to circulate the etching liquid over the surface of the material to be etched, and possibly low-frequency sound waves, between 1 and 40 kHz, in order to improve mixing. For example, in document U.S. Pat. No. 4,544,066, the solution is agitated by low-frequency ultrasound in order to even out the reaction over the surface.